aoc2025/07/code.go

package main

import (
	"bufio"
	"fmt"
	"log"
	"os"
)

func readInput(file *os.File) ([]string, int) {
	scanner := bufio.NewScanner(file)
	var maze []string
	start := -1

	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			continue
		}

		if start < 0 {
			for i := range line {
				if line[i] == 'S' {
					start = i
					break
				}
			}
		}

		maze = append(maze, line)
	}

	return maze, start
}

func part1(maze []string, beams []int) int {
	var count int

	for row := 1; row < len(maze); row++ {
		for i := range beams {
			if beams[i] == 0 {
				continue
			}

			if maze[row][i] == '^' {
				if i > 0 {
					beams[i-1]++
				}

				if i < len(beams)-1 {
					beams[i+1]++
				}

				beams[i] = 0

				count++
			}
		}
	}

	return count
}

func part2(maze []string, beams []int) int {
	for row := 2; row < len(maze); row += 2 {
		for i := range beams {
			if beams[i] == 0 {
				continue
			}

			if maze[row][i] == '^' {
				beams[i-1] += beams[i]
				beams[i+1] += beams[i]

				beams[i] = 0
			}
		}
	}

	var count int
	for _, b := range beams {
		count += b
	}

	return count
}

func main() {
	if len(os.Args) < 2 {
		log.Fatal("You need to specify a file!")
	}

	filePath := os.Args[1]
	file, err := os.Open(filePath)
	if err != nil {
		log.Fatalf("Failed to open %s!\n", filePath)
	}

	maze, start := readInput(file)
	beams := make([]int, len(maze[0]))
	beams[start] = 1
	fmt.Println("Part1:", part1(maze, beams))

	beams2 := make([]int, len(maze[0]))
	beams2[start] = 1
	fmt.Println("Part2:", part2(maze, beams2))
}